Find Matches Review

class Trie:
    def find_matches(self, document: str) -> set[str]:
        matches = set()
        for i in range(len(document)):
            level = self.root
            for j in range(i, len(document)):
                ch = document[j]
                if ch not in level:
                    break
                level = level[ch]
                if self.end_symbol in level:
                    matches.add(document[i : j + 1])
        return matches